This application is the competitive renewal for a three year extension of a randomized, double-blinded, clinical trial (1) to evaluate the growth-promoting properties of 1,25-dihydroxyvitamin D versus dihydrotachysterol in children with mild to moderate chronic renal insufficiency and (2) to investigate the important therapeutic question of hypercalcemia and accelerated deterioration of renal function, secondary to the use of one or both of the vitamin D metabolites. Secondary aims include health of children with early chronic renal insufficiency by careful examination of variables of interest in the control period of he study. The feasibility study of this multi-center trial took 1.5 years to complete. During the subsequent 3.5 years (12/84-5/88) of patient accrual, 94 patients entered this study, and 27 patients exited. However, 11 of the study exits have completed 6 moths of control and 6 months of treatment data collection; thus, 78 patients have completed the minimal periods of the study in 3.5 years. This represents a net gain of 22 patients per year, taking into account the current rate of study exits. If this rate of net patient accrual is maintained for two additional years (4/1/88- 3/31/90) with 4/1/90-3/31/91 for follow-up, the Study will have a newt gain of 44 patients, resulting in a net total of 122 patients, on whom 6 months of control and at least 6 months data will have been obtained. The current resubmission for a three year extension (4/1/89- 3/31/92) will permit completion of patient follow-up by mid-1991 and the final year (4/1/91-3/31/93) devoted to analysis of the complete data and preparation for the final reports.